The aforesaid cutting and/or sawing unit is a development of an earlier, less refined cutting unit of the kind described, for instance, in Swedish Patent Application No. 89103434-2. This known unit is provided with a saw blade which is mounted on a motor stand and fitted with two knives and is intended to rotate in the close proximity of a toothed device, thereby obtaining a cutting action between the knives and the cutting surfaces of the teeth on said device. This unit is able to cut everything from grass and thick-stalk plants to thickets and bushes, shrubs, having stem thickness of up to 5 cm.
However, thicket and bush vegetation which is to be cleaned and cleared will often contain slender threes which must be cut manually with the aid of some type of motor saw. With the intention of eliminating such manual work when cleaning areas of this nature, the number of knives on the saw blade of some cutting units has been increased so as to obtain a sawing action which will enable thicker stems to be cut. However, it is necessary to exercise caution when cutting or felling relatively thick stems, since if the cutting unit is brought against a stem too quickly, the stem is liable to be drawn in towards the center of the saw blade and wedge there between a cutting knife and a cutting tooth, causing the blade to stop abruptly. In order to prevent wood which is too thick to be cut by the unit from being drawn into the cutting unit, there is described in Swedish Patent Application No. 9002286-4 a saw which is equipped with knives whose forward cutting edges are provided with stepped projections. A saw of this construction will not only prevent wood from being drawn into the cutting unit, but also has a lower power consumption than other units while being capable of cutting vegetation of stem thicknesses in the region of 15-20 cm. This extension of the working range of the unit to include trees which can be used in the manufacture of wood chips and wood pulp results in the need of a rational and effective method of recovering the coarser part of the wood when cleaning and thinning vegetation.